Low energy switching is unreliable unless special precautions are taken to insure the breakdown of an insulating film that forms on the surface of the switch contacts. In the prior art, redundant contacting in each switch is provided, and, sometimes, a double wipe contact may be used with high contact pressure to insure that when a switch is closed, the insulating film which tends to form over the contact will break down, thereby insuring conduction. (See, e.g., AMF MA-012-DW Series switches.)
Input circuits such as CMOS logic circuits require extremely small currents at low voltages so that activating an input switch does not always result in a reliable contact being made because the insulating film, which may be due to oxidation of the contact surface, is not broken down by the extremely low energy being switched.
Another prior art solution is to use a constant current generator to provide higher energy through the switch contacts. This, however, increases the cost of providing input switching. Also, switching contacts have been designed so that, when the switch is closed, the contact area is small which increases the closure current density to aid film breakdown.
The invention described herein provides an inexpensive circuit for insuring the breakdown of the insulation layer on an inexpensive switch used in low energy applications by placing a high voltage across the switch and yet maintaining the desired output voltage swing.